Ethylene/.alpha.-olefin/nonconjugated polyene random copolymers (hereinafter also simply referred to as ethylene copolymerized rubber) such as ethylene/.alpha.-olefin/polyene terpolymer (EPDM) and the like copolymers have been widely used as materials for automobiles, electric wires, construction and civil engineering, and as industrial materials owing to their excellent weatherability, resistance against ozone and thermal aging resistant property.
In recent years, it has been urged to produce ethylene/.alpha.-olefin/nonconjugated polyene random copolymers having further improved thermal aging resistance properties and high fluidity (high-speed moldability) for use in the above-mentioned applications.
It has been known that an ethylene/propylene/dicyclopentadiene (DCPD) copolymerized rubber exhibits higher fluidity (higher-speed moldability) than the ethylene/propylene/ethylidenenorbornene (ENB) copolymerized rubbers or the ethylene/propylene/1,4-hexadiene copolymerized rubbers.
It has further been known to greatly increase the thermal aging resistant property by effecting the crosslinking by using an organic peroxide instead of using sulfur which is a generally used curing agent.
Generally, however, the organic peroxide is very expensive compared to sulfur. When the organic peroxide is used in small amounts in order to suppress the cost, the ethylene/propylene/ethylidenenorbornene (ENB) copolymerized rubber, ethylene/propylene/1,4-hexadiene copolymerized rubber and ethylene/propylene/dicyclopentadiene (DCPD) are all loosely crosslinked and exhibit poor mechanical properties.
It has therefore been desired to provide an ethylene/.alpha.-olefin/nonconjugated polyene random copolymer which maintains excellent mechanical properties even when the organic peroxide is used in small amounts and exhibits excellent thermal aging resistant property and excellent fluidity (high-speed moldability), as well as to provide a rubber composition thereof and a process for its preparation.
In view of the above-mentioned prior art, the present inventors have conducted keen study concerning an ethylene/.alpha.-olefin/nonconjugated polyene random copolymer and a process for its preparation, and have succeeded in producing an ethylene/.alpha.-olefin/nonconjugated polyene random copolymer of quite a novel structure.
It is an object of the present invention to provide an ethylene/.alpha.-olefin/nonconjugated polyene random copolymer having a novel structure and excellent fluidity, crosslinking property with peroxide, thermal aging resistant property and mechanical properties, that could not be obtained by the traditional preparation methods, and a process for its preparation.
Another object of the present invention is to provide an ethylene random copolymerized rubber composition which has a low tackiness on the surface of the crosslinked product, does not abnormally produce foam in the inside, and yields a crosslinked product having excellent thermal aging resistant property and resistance against permanent strain and, particularly, to provide a rubber composition for hot-air crosslinking.